(1) Field of the Invention
The present invention relates to semiconductor devices and methods for fabricating the same, and more particularly relates to a semiconductor device including MIS transistors of different conductivity types.
(2) Description of Related Art
In recent years, with increases in the degree of integration, functionality and speed of semiconductor integrated circuit devices, miniaturization of transistors has been advanced. A so-called scaling law in which the current driving forces of transistors are improved with advances in miniaturization of transistors has been conventionally effective. Meanwhile, in order to achieve reduction in energy consumption and the long-time use of mobile devices, further miniaturization of transistors and reduction in power consumption have been demanded. In such a field, decreases in the sizes of transistors do not lead to improvement in the driving forces of transistors.
In order to improve the driving force of a transistor, a measure in which a gate insulating film is reduced in thickness is considered. However, a problem that a reduction of the thickness of a gate insulating film causes gate leakage current to increase occurs. To cope with this, a technique has been suggested in which the driving force of a transistor is improved by applying stress to a channel region of the transistor (see, for example, S. Ito, et al., “IEDM 2000”, 2000, p. 247).
FIG. 6 illustrates a cross-sectional structure of a known transistor having a structure in which stress is applied to a channel region of the transistor. As illustrated in FIG. 6, a gate electrode 204 is formed on a substrate 201 with a gate insulating film 203 interposed therebetween, L-shaped first sidewalls 206 are formed on both lateral sides of the gate electrode 204, and second sidewalls 207 are formed on both lateral sides of the gate electrode 204 with the first sidewalls 206 interposed therebetween. A liner insulating film 209 is formed to cover the gate electrode 204 and the second sidewalls 207. The liner insulating film 209 represents a film having tensile stress. With the above-described structure, stress can be applied to the channel region under the gate electrode 204, resulting in the driving force of the transistor improved.
However, for the known semiconductor device, stress arising from the liner insulating film 209 is not sufficiently transferred to the channel region, and thus the driving force of the transistor cannot be sufficiently improved.
Furthermore, a memory unit or any other unit requires both a P-channel transistor and an N-channel transistor. Meanwhile, the orientation of stress needed to improve the driving force of a P-channel transistor is different from that of stress needed to improve the driving force of an N-channel transistor. In view of the above, if a liner insulating film having tensile stress were formed to improve the driving force of an N-channel transistor, the driving force of a P-channel transistor would be reduced. In order to avoid the reduction in the driving force of the P-channel transistor, the step of removing a part of the liner insulating film located on a region of the substrate on which the P-channel transistor is to be formed (hereinafter, referred to as “P-channel transistor formation region), the step of forming a mask to prevent the formation of a liner insulating film on the P-channel transistor formation region, or any other step is needed.